The present invention relates to an anti-skid device for preventing an automobile tire from its slippage, and more particularly, to a type thereof wherein anti-skid members project from the retract into a road contacting surface of the tire in accordance with changeable road surface conditions.
The road surface condition is frequently changed by the weather conditions, localities, sunny or shadow place, daytime or night time. The road surface condition is particularly changed during early winter season, and early spring season. For example, the road surface is covered with snow, or freezing or icy or dry road surface may result.
Conventionally, during snow falling season, a chain is mounted over an automobile tire to prevent slippage accident. Alternatively, an ordinary tire is replaced by a spiked or studded tire. Further, various types of apparatus have been proposed in which anti-skid members is projectable from and retractable into a road contacting surface of the tire.
The chain is effective for preventing tire from slippage against road surface covered with heavy snow or against frozen road surface. However, rather high skill is required for mounting the chain over the tire. It would be difficult and troublesome for the mounting work under bad weather condition such as heavy snow falling and snowdrift. Further, the chain mounted tire may degrade runing comfortableness, and may disadvantageously provide sideslip and skidding. Therefore, the chain-mounted tire may provide degradation of safty. Furthermore, the chain may be broken, if the vehicle runs for a prolonged period on a frozen road surface which is a border to the noncovered and nearly exposed road surface.
The spiked tire would be inferior to the chain-mounted tire when the vehicle runs on a heavily snow-covered road, while the spiked tire is available for running on frozen road or compressed snow covered road. However, as described above, the road surface condition is changeable, particularly during early winter and early spring seasons. For example, the snow may be melted and road surface is dried, or there are several icy portions on the road.
If the vehicle with the chain-mounted tires or spiked tires runs on road whose surface is exposed to the atmosphere, noise is generated, and the road surface is excessively damaged. The damaged surface may cause public pollution such as particle ladden atmosphere. For this, there are several regulations which prohibits the use of spiked tire in West Germany, Norway, Sweden, Holland, Miyagiprefecture Japan, etc. If the operator removes or mounts the chain or exchanges the spiked tire by the normal tire and vice versa in accordance with the change of the road surface, such public pollution can be obviated. However, chain removal and attachment work and tire replacement work may require about 20 to 30 minutes for a skilled operator, and it would be rather impossible to conduct such work in accordance with the road surface chage, since the road surface is frequently changeable by weather condition, localities, and time.
In order to overcome the above-described drawbacks, proposed were various device which allow spike pins to project from the retract into a road contacting surface of the tire. However, so far, no actual device has been put into practice.
This types of device is described in, for example, Japanese Utility Model Publication No. 52-3762, Japanese Patent Application Publication (Kokai) Nos. 50-83902, 53-133801 and 53-104908. In these publications, spike pins themselves directly projects out of the tire. Particularly, according to the publication Nos. 50-83902, 53-133801 and 53-104908, each of the spike pins is connected with projecting mechanism.
In the conventional spiked tire, it is necessary to embed about 100 to 150 number of spike pins at a tread portion of the road contact surface of the tire. In the device wherein the spike pins directly project out of the tire, required are water proof, dust proof and air-tight structure for holes which allow spike pins to pass therethrough. However, there is no structure which can fullfil these requirements. Therefore, various disadvantages are caused, and it would be doubtful whether or not the spike pins surely project from and retract into the tire during actual running of the vehicle. Even if water proof means is provided at the holes, frictional resistance may be increased between the spike pins and the holes, which resistance may render the spike pin incapable of its projection and retraction.
In another aspect, when the vehicle with installed spiked tires runs for a long time on the mountain road on which thin frozen ice is covered, relatively large amount of frictional heat is generated between the spike pins and the road surface. Therefore, rust may be generated at the spike pins due to high frictional heat and water or moisture, and as a result, it becomes impossible to project and retract the pins from and into the tire. Further, the heat is transmitted to the mechanism for moving the spike pins through each of the bottom portions of flanges of the spike pins, so that the mechanism per se becomes inoperable.
Moreover, since the tire portions each adjacent to holes which allow the spike pins to pass therethrough are subjected to heavy shearing force, so that the portions may be damaged by the shearing force. In order to sustain the shearing force and to obtain sufficient mechanical strength, proposed is the reinforcement of each of the holes. However, such reinforcement may lead to complicated production process, and resultant tire becomes heavy, which is not available for practicality. Even if the reinforcement is made, movement of the spike pins in radial direction of the tire becomes impossible, when the spike pin is slightly deformed due to heavy shearing force and strong impacting force against the road surface in projecting out state of the pins.
Another type of spike pin projection structure is proposed wherein each one of the pins is subjected to projection and retraction among a plurality of pins. According to this structure, complicated fluid paths (fluid pressure circuit) is required in the tire, and therefore, actual practicality would be dubious.
According to still another type, flange bottom portions of the respective spike pins are directly or indirectly communicates with bores of the pressure circuit which drives the pins for their radial movement relative to the tire. However, if strong shearing force and impact force is applied from the road surface to one of the spike pins, pressure leakage may occur at the one of the pins, so that resultant device becomes inoperable.
According to the publication Nos. 50-83902 and 53-133801, each of the spike pins is provided with mechanically projecting-out mechanism. However, the mechanism is complicated, and it would be difficult to put it into actual practice.
According to the publication No. 53-104908, mechanism for projecting and retracting the spike pins extends through a carcass and breaker portions of the tire. Therefore, there is technical problems in terms of sealability and mechanical strength at these portions. Further, tire strength per se may be lowered. More specifically, mechanical strength and pressure resistivity of the tire is generally obtained by the carcass and breaker portions. However, a plurality of bores are formed for the projecting-out mechanism at the very important portions according to the publication. Therefore, water proof efficiency and fluid tightness may be lowered, and tire strenth itself is degraded due to the formation of the bore at the carcass and the breaker. Such tire is not available for actual use.
Despite the fact that these device are used in cold season, there are no countermeasure against use in the cold season. For this, if the ambient temperature becomes less than the freezing point, moisture in air confined in the device may be frozen, to thereby render the device inoperable.